# Repeatedly trying to start a failed car battery - dangerous? **URL:** \ **Category:** Factual Questions\ **Created:** [November 15, 2015, 9:08pm UTC](https://boards.straightdope.com/t/repeatedly-trying-to-start-a-failed-car-battery-dangerous/737647 "2015-11-15T21:08:00Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![Velocity](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/velocity/32/18006_2.png) [@Velocity](https://boards.straightdope.com/u/Velocity)\ **Post date:** [November 15, 2015, 9:08pm UTC](https://boards.straightdope.com/t/repeatedly-trying-to-start-a-failed-car-battery-dangerous/737647/1 "2015-11-15T21:08:00Z")
My car battery is dead. Unfortunately, being the obstinate person that I am, I tried over a dozen times to turn the key in the ignition, simply resulting in “dead battery sounds.” I’m going to jump start it, but did I do anything dangerous to the battery by trying to start it the normal way repeatedly? Are there now any hazards in jump starting the battery after I metaphorically beat the dead horse? ---
**Author:** ![Velocity](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/velocity/32/18006_2.png) [@Velocity](https://boards.straightdope.com/u/Velocity)\ **Post date:** [November 15, 2015, 9:11pm UTC](https://boards.straightdope.com/t/repeatedly-trying-to-start-a-failed-car-battery-dangerous/737647/2 "2015-11-15T21:11:21Z")
(This is a need answer fast question.) ---
**Author:** ![TriPolar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tripolar/32/3008_2.png) [@TriPolar](https://boards.straightdope.com/u/TriPolar)\ **Post date:** [November 15, 2015, 9:17pm UTC](https://boards.straightdope.com/t/repeatedly-trying-to-start-a-failed-car-battery-dangerous/737647/3 "2015-11-15T21:17:14Z")
Batteries don’t do so well after they’ve been fully discharged. So that might shorten it’s life but if it’s not about to die of old age it’s probably fine once you get it charged up. BTW: if you provide the year, make, and model the pros on the board could tell you about any other problems you might have after discharging your battery. ---
**Author:** ![Nefario](https://avatars.discourse-cdn.com/v4/letter/n/59ef9b/32.png) [@Nefario](https://boards.straightdope.com/u/Nefario)\ **Post date:** [November 15, 2015, 9:37pm UTC](https://boards.straightdope.com/t/repeatedly-trying-to-start-a-failed-car-battery-dangerous/737647/4 "2015-11-15T21:37:51Z")
> [@Velocity](#): > > (This is a need answer fast question.) Fast Answer - No It should jump start and run OK if it has been previously doing so. ---
**Author:** ![Velocity](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/velocity/32/18006_2.png) [@Velocity](https://boards.straightdope.com/u/Velocity)\ **Post date:** [November 15, 2015, 9:45pm UTC](https://boards.straightdope.com/t/repeatedly-trying-to-start-a-failed-car-battery-dangerous/737647/5 "2015-11-15T21:45:43Z")
> [@TriPolar](#): > > Batteries don’t do so well after they’ve been fully discharged. So that might shorten it’s life but if it’s not about to die of old age it’s probably fine once you get it charged up. > > BTW: if you provide the year, make, and model the pros on the board could tell you about any other problems you might have after discharging your battery. 2009 SmartCar. ---
**Author:** ![Carl\_Pham](https://avatars.discourse-cdn.com/v4/letter/c/e9a140/32.png) [@Carl\_Pham](https://boards.straightdope.com/u/Carl_Pham)\ **Post date:** [November 15, 2015, 9:50pm UTC](https://boards.straightdope.com/t/repeatedly-trying-to-start-a-failed-car-battery-dangerous/737647/6 "2015-11-15T21:50:37Z")
No. When you complete the circuit and the battery is dead, very little current flows, so nothing much happens. You’re going to stress the battery much more when you jump-start the car, because large currents will flow. Nevertheless, lead-acid batteries are generally much more robust than the batteries in consumer electronics, and this kind of abuse generally won’t faze them. ---
**Author:** ![jz78817](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jz78817/32/1028_2.png) [@jz78817](https://boards.straightdope.com/u/jz78817)\ **Post date:** [November 15, 2015, 11:47pm UTC](https://boards.straightdope.com/t/repeatedly-trying-to-start-a-failed-car-battery-dangerous/737647/7 "2015-11-15T23:47:37Z")
it depends on how deeply you ran it flat. when you discharge a lead-acid battery, a layer of lead sulfate starts building up on the plates. discharge it too deeply, the layer can get thick enough to both damage the plates, and be enough of a barrier to conduction where you won’t be able to charge the battery much if at all. ---
**Author:** ![GreasyJack](https://avatars.discourse-cdn.com/v4/letter/g/df705f/32.png) [@GreasyJack](https://boards.straightdope.com/u/GreasyJack)\ **Post date:** [November 15, 2015, 11:59pm UTC](https://boards.straightdope.com/t/repeatedly-trying-to-start-a-failed-car-battery-dangerous/737647/8 "2015-11-15T23:59:00Z")
Although if the problem isn’t actually a dead battery but instead a damaged or loose battery cable then, yes, there is some small but existent risk of starting a fire by repeatedly trying to start it. ---
**Author:** ![Gbro](https://avatars.discourse-cdn.com/v4/letter/g/c6cbf5/32.png) [@Gbro](https://boards.straightdope.com/u/Gbro)\ **Post date:** [November 16, 2015, 12:21am UTC](https://boards.straightdope.com/t/repeatedly-trying-to-start-a-failed-car-battery-dangerous/737647/9 "2015-11-16T00:21:25Z")
It might depend on how you went about your dozen attempts were done and of course how dead the battery actually was. If you turned the ignition key fully off each time you tried and the battery had enough energy to run the fuel pump each time you could flood t e engine and that could also lead to fuel in the oil. And of course this jumping often is going to take a toll on your alternator. ---
**Author:** ![Velocity](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/velocity/32/18006_2.png) [@Velocity](https://boards.straightdope.com/u/Velocity)\ **Post date:** [November 17, 2015, 6:24pm UTC](https://boards.straightdope.com/t/repeatedly-trying-to-start-a-failed-car-battery-dangerous/737647/10 "2015-11-17T18:24:29Z")
> [@Gbro](#): > > It might depend on how you went about your dozen attempts were done and of course how dead the battery actually was. > If you turned the ignition key fully off each time you tried and the battery had enough energy to run the fuel pump each time you could flood the engine and that could also lead to fuel in the oil. Interesting - how bad would this be? ---
**Author:** ![Gary\_T](https://avatars.discourse-cdn.com/v4/letter/g/3ec8ea/32.png) [@Gary\_T](https://boards.straightdope.com/u/Gary_T)\ **Post date:** [November 17, 2015, 7:00pm UTC](https://boards.straightdope.com/t/repeatedly-trying-to-start-a-failed-car-battery-dangerous/737647/11 "2015-11-17T19:00:42Z")
> [@Gbro](#): > > If you turned the ignition key fully off each time you tried and the battery had enough energy to run the fuel pump each time you could flood t e engine and that could also lead to fuel in the oil. No, unless the engine is turning over the injectors won’t operate and no fuel will go to into the cylinders. The fuel pump will just pressurize the lines. ---
**Author:** ![GreasyJack](https://avatars.discourse-cdn.com/v4/letter/g/df705f/32.png) [@GreasyJack](https://boards.straightdope.com/u/GreasyJack)\ **Post date:** [November 17, 2015, 7:00pm UTC](https://boards.straightdope.com/t/repeatedly-trying-to-start-a-failed-car-battery-dangerous/737647/12 "2015-11-17T19:00:44Z")
Attempting to start a car that won’t turn over at all certainly won’t flood it. The fuel pump only builds pressure; the injectors won’t actually open until the engine is turning. Trying to start a car with a weak battery could theoretically flood the engine if you’re getting weak spark, but usually it’ll go from weak cranking to no cranking before flooding becomes an issue. ETA: ninja’ed! ---
**Author:** ![herman\_and\_bill](https://avatars.discourse-cdn.com/v4/letter/h/f1d935/32.png) [@herman\_and\_bill](https://boards.straightdope.com/u/herman_and_bill)\ **Post date:** [November 17, 2015, 7:19pm UTC](https://boards.straightdope.com/t/repeatedly-trying-to-start-a-failed-car-battery-dangerous/737647/13 "2015-11-17T19:19:13Z")
You probably didn’t, but, you can damage your starter by trying to start your car with a “dead” battery. When the voltage drops because of a dead battery, the current flow will increase, which can burn the windings in the starter. See Ohms law. ---
**Author:** ![bob\_2](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bob_2/32/3341_2.png) [@bob\_2](https://boards.straightdope.com/u/bob_2)\ **Post date:** [November 17, 2015, 7:24pm UTC](https://boards.straightdope.com/t/repeatedly-trying-to-start-a-failed-car-battery-dangerous/737647/14 "2015-11-17T19:24:33Z")
In my experience, a completely flat car battery is dead, expired, kicked the bucket, shuffled off its mortal coil, run down the curtain and joined the bleedin’ choir invisibile!! THIS IS AN EX-battery!! Oops - got a bit pythonesque there but you get my drift. ---
**Author:** ![Gary\_T](https://avatars.discourse-cdn.com/v4/letter/g/3ec8ea/32.png) [@Gary\_T](https://boards.straightdope.com/u/Gary_T)\ **Post date:** [November 17, 2015, 7:54pm UTC](https://boards.straightdope.com/t/repeatedly-trying-to-start-a-failed-car-battery-dangerous/737647/15 "2015-11-17T19:54:44Z")
> [@herman\_and\_bill](#): > > When the voltage drops because of a dead battery, the current flow will increase, which can burn the windings in the starter. See Ohms law. I think you got a bit mixed up there. Ohm’s Law: E=I•R. With no change in resistance (R), if voltage (E) drops then amperage (I) (= current flow) must also drop. ---
**Author:** ![herman\_and\_bill](https://avatars.discourse-cdn.com/v4/letter/h/f1d935/32.png) [@herman\_and\_bill](https://boards.straightdope.com/u/herman_and_bill)\ **Post date:** [November 17, 2015, 9:34pm UTC](https://boards.straightdope.com/t/repeatedly-trying-to-start-a-failed-car-battery-dangerous/737647/16 "2015-11-17T21:34:44Z")
> [@Gary\_T](#): > > I think you got a bit mixed up there. Ohm’s Law: E=I•R. With no change in resistance (R), if voltage (E) drops then amperage (I) (= current flow) must also drop. Nope. This is because the power needed by the starter is constant, and power = voltage x current. So if voltage goes down, current must go up to compensate. ---
**Author:** ![Velocity](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/velocity/32/18006_2.png) [@Velocity](https://boards.straightdope.com/u/Velocity)\ **Post date:** [November 17, 2015, 10:37pm UTC](https://boards.straightdope.com/t/repeatedly-trying-to-start-a-failed-car-battery-dangerous/737647/17 "2015-11-17T22:37:26Z")
> [@GreasyJack](#): > > Attempting to start a car that won’t turn over at all certainly won’t flood it. The fuel pump only builds pressure; the injectors won’t actually open until the engine is turning. Trying to start a car with a weak battery could theoretically flood the engine if you’re getting weak spark, but usually it’ll go from weak cranking to no cranking before flooding becomes an issue. > > ETA: ninja’ed! Ok, if it flooded, what to do…oil change? ---
**Author:** ![Gary\_T](https://avatars.discourse-cdn.com/v4/letter/g/3ec8ea/32.png) [@Gary\_T](https://boards.straightdope.com/u/Gary_T)\ **Post date:** [November 18, 2015, 12:04am UTC](https://boards.straightdope.com/t/repeatedly-trying-to-start-a-failed-car-battery-dangerous/737647/18 "2015-11-18T00:04:28Z")
> [@herman\_and\_bill](#): > > Nope. This is because the power needed by the starter is constant… …but the power the battery is able to provide is not in this case – we’re talking about a battery that can’t operate the starter. ---
**Author:** ![Velocity](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/velocity/32/18006_2.png) [@Velocity](https://boards.straightdope.com/u/Velocity)\ **Post date:** [November 18, 2015, 12:05am UTC](https://boards.straightdope.com/t/repeatedly-trying-to-start-a-failed-car-battery-dangerous/737647/19 "2015-11-18T00:05:35Z")
> [@Gary\_T](#): > > No, unless the engine is turning over the injectors won’t operate and no fuel will go to into the cylinders. The fuel pump will just pressurize the lines. The engine was making sound, though. ---
**Author:** ![GreasyJack](https://avatars.discourse-cdn.com/v4/letter/g/df705f/32.png) [@GreasyJack](https://boards.straightdope.com/u/GreasyJack)\ **Post date:** [November 18, 2015, 1:31am UTC](https://boards.straightdope.com/t/repeatedly-trying-to-start-a-failed-car-battery-dangerous/737647/20 "2015-11-18T01:31:40Z")
> [@Velocity](#): > > The engine was making sound, though. What kind of sounds? To me “dead battery sounds” usually means the clickclickclickclickclick noise which is the solenoid trying to engage the starter but failing. So in that case, the engine isn’t actually being turned and so the injectors aren’t firing. The situation I was describing is if the engine is cranking over like normal, just much slower and unevenly. But that usually happens when the battery is just barely on the cusp of being too dead to turn the engine over and so after a try or two either the car will start or the battery won’t even be able to do even that and you get the clickclickclickclickclick. The flooding situation is incredibly unlikely (on a modern car at least) so don’t worry about it. [Next page](https://boards.straightdope.com/t/repeatedly-trying-to-start-a-failed-car-battery-dangerous/737647.md?page=2)